.TH IRDPD 8
.SH NAME
irdpd \- internet router discovery protocol daemon
.SH SYNOPSIS
.B irdpd
.RB [ \-bsd ]
.RB [ \-U
.IR udp-device ]
.RB [ \-I
.IR ip-device ]
.RB [ \-o
.IR priority-offset ]
.SH DESCRIPTION
.B Irdpd
looks for routers.  This should be a simple task, but many routers are hard
to find because they do not implement the router discovery protocol.  This
daemon collects information that routers do send out and makes it available.
.PP
At startup
.B irdpd
sends out several router solicitation broadcasts.  A good router should
respond to this with a router advertisement.
.PP
If a router advertisement arrives then no more solicitations are sent.  The
TCP/IP server has filled its routing table with the info from the
advertisement, so it now has at least one router.  If the advertisement is
sent by a genuine router (the sender is in the table) then the
.B irdpd
daemon goes dormant for the time the advert is valid.  Routers send new
adverts periodically, keeping the daemon silent.
.PP
Otherwise
.B irdpd
will listen for RIP (Router Information Protocol) packets.  These packets
are sent between routers to exchange routing information.
.B Irdpd
uses this information to build a routing table.
.PP
Every now and then a router advertisement is sent to the local host to give
it router information build from the RIP packets.
.PP
Lastly, if a router solicitation arrives and there is no router around that
sends advertisements, then
.B irdpd
sends an advertisement to the requestor.  Note that this is a direct violation
of RFC1256, as no host is supposed to sent those adverts.  But alas the world
is not always perfect, and those adverts make booting hosts find routers
quickly with this help from their brothers.  (Of course, they will lose the
router soon if they don't have an
.B irdpd
daemon themselves.)
.SH OPTIONS
.TP
.B \-b
Broadcast advertisements instead of sending them to the local host only.
This may be used to keep (non-Minix) hosts alive on a net without adverts.
.TP
.B \-s
Be silent, do not send advertisements to hosts that ask for them.
.TP
.B \-d
Debug mode, tell where info is coming from and where it is sent.  Debugging
can also be turned on at runtime by sending signal
.B SIGUSR1
or turned off with
.BR SIGUSR2 .
.TP
.BI \-o " priority-offset
Offset used to make the gateway's preferences collected from RIP packets look
worse than those found in genuine router adverts.  By default
.BR -1024 .
.SH "SEE ALSO"
.BR set_net_default (8),
.BR boot (8),
.BR inetd (8),
.BR nonamed (8),
.BR rarpd (8).
.SH BUGS
Under standard Minix this daemon can't listen to two both IRDP and RIP
at the same time, so it starts out with IRDP.  It switches over to RIP
if it can't find a router, or if it threatens to lose its router.  It
does not switch back.
.PP
.B Irdpd
may help a host that should not be helped, i.e. if it doesn't have an
.B irdpd
daemon with RIP collecting trickery.  It will make System Administrators
pull out their remaining hair trying to find out why a host can access
outside networks for a some time after boot, but goes blind afterwards.
.SH AUTHOR
Kees J. Bot (kjb@cs.vu.nl)
